Semiconductor Light Detecting Element and Manufacturing Method Thereof

ABSTRACT

A semiconductor photodetector device (PD 1 ) comprises a multilayer structure (LS 1 ) and a glass substrate ( 1 ) optically transparent to incident light. The multilayer structure includes an etching stop layer ( 2 ), an n-type high-concentration carrier layer ( 3 ), an n-type light-absorbing layer ( 5 ), and an n-type cap layer ( 7 ) which are laminated. A photodetecting region ( 9 ) is formed near a first main face ( 101 ) of the multilayer structure, whereas a first electrode ( 21 ) is provided on the first main face. A second electrode ( 27 ) and a third electrode ( 31 ) are provided on a second main face ( 102 ). A film ( 10 ) covering the photodetecting region and first electrode is formed on the first main face. A glass substrate ( 1 ) is secured to the front face ( 10   a ) of this film.

TECHNICAL FIELD

The present invention relates to a semiconductor photodetector deviceand a method of manufacturing the same.

BACKGROUND ART

Recently, as the CPU driving frequency has been becoming higher (e.g.,10 GHz or higher), attention has been directed toward opticalinterconnection techniques in which signals within and between systemapparatus are transmitted by light. Semiconductor devices such assemiconductor photodetector devices and semiconductor light-emittingdevices are used in the optical interconnection techniques.

When mountability to external substrates is concerned in a semiconductorphotodetector device used in the optical interconnection techniques, itwill be preferred if an electrode (signal electrode) for taking outsignals from the photodetector device is arranged on a surface oppositefrom a light-incident surface. Examples of such semiconductorphotodetector devices are disclosed in Japanese Patent ApplicationLaid-Open Nos. HEI 3-104287, HEI 6-296035, and 2002-353564. Thesepublications disclose semiconductor photodetector devices ofback-illuminated type in which a plurality of compound semiconductorlayers are formed on one main face side of a semiconductor substrate,while light is incident from the other main face side.

For the following purposes, these back-illuminated semiconductorphotodetector devices partly thin the portion of the substrate locatedunder the photodetecting part, while surrounding this portion with apart maintaining the thickness of the substrate. The first purpose is toprevent signals from deteriorating or disappearing because of lightabsorption by the semiconductor substrate. The second purpose is toprevent the semiconductor photodetector devices from being damaged orbroken when mounting the semiconductor photodetector devices ontoexternal substrates by wire bonding or bump bonding.

However, there is a limit to reducing the size of the above-mentionedback-illuminated semiconductor photodetector devices, since there is aportion maintaining the substrate thickness in order to keep mechanicalstrength. When forming an array of semiconductor photodetector devicesby providing a plurality of photodetecting parts in particular, thepitch between the photodetecting parts is hard to narrow, whereby thesemiconductor photodetector device array must increase its size.

DISCLOSURE OF THE INVENTION

It is the object of the present invention to provide a semiconductorphotodetector device which can be made smaller while keeping asufficient mechanical strength, and a method of manufacturing the same.

In one aspect, the present invention relates to a semiconductorphotodetector device. This photodetector device comprises a multilayerstructure including a plurality of compound semiconductor layerslaminated and having first and second main faces opposing each other; aphotodetecting region formed near the first main face within themultilayer structure; a first electrode arranged on the first main faceof the multilayer structure and electrically connected to thephotodetecting region; a second electrode arranged on the second mainface of the multilayer structure and electrically connected to the firstelectrode; a third electrode arranged on the second main face of themultilayer structure and electrically connected to a part near thesecond main face in the multilayer structure; and a light-transmittinglayer, optically transparent to incident light and arranged on the firstmain face of the multilayer structure, covering the photodetectingregion and first electrode.

In this photodetector device, the mechanical strength of the multilayerstructure is held by the light-transmitting layer even when a pluralityof compound semiconductor layers included in the multilayer structureare made thinner. Unlike the prior art mentioned above, there is no needto form a part maintaining the substrate thickness, whereby the deviceis easily made smaller.

In this photodetector device, the second and third electrodes for takingout output signals are arranged on the second main face of themultilayer structure. Therefore, the photodetector device can be mountedwhile its second main face positioned on the opposite side of thephotodetecting region opposes a mounting surface of an externalsubstrate or the like. As a result, the photodetector device can bemounted easily.

The light-transmitting layer may include a film made of silicon oxideand a glass substrate. The glass substrate may be secured to themultilayer structure through the film made of silicon oxide. Siliconoxide can be fused to glass, and thus can bond the multilayer structureand glass substrate to each other without using other adhesives.Therefore, the light incident on the glass substrate side can reach themultilayer structure without being absorbed by adhesives.

The light-transmitting layer may include a film made of silicon oxide ora resin without a glass substrate.

The plurality of compound semiconductor layers may include ahigh-concentration carrier layer of a first conductive type, alight-absorbing layer of the first conductive type, and a cap layer ofthe first conductive type. The photodetecting region may be a region ofa second conductive type including at least a part of the cap layer.

The multilayer structure may further comprise a depression formed aboutthe photodetecting region, and a wiring electrode arranged within thedepression. The first electrode may be electrically connected to thesecond electrode through the wiring electrode. The third electrode maybe electrically connected to a part positioned near the photodetectingregion in the high-concentration carrier layer. The depression formedabout the photodetecting region separates the photodetecting region atleast partly from the other parts of the multilayer structure, and thuscan reduce parasitic capacitance by a greater amount. When the wiringelectrode arranged in the depression is utilized as a through electrodepenetrating through the multilayer structure, the through electrode canbe formed very easily. When the through electrode is used, the electrodeis directly drawn from the high-concentration carrier layer of thephotodetecting part, whereby the series resistance can be reducedgreatly.

The photodetector device of the present invention may further comprise athrough lead penetrating through the multilayer structure. The firstelectrode may be electrically connected to the second electrode throughthe through electrode. The third electrode may be electrically connectedto the high-concentration carrier layer. In this case, the through leadcan electrically connect the first and second electrodes to each otherreliably. Since the electrode is directly drawn from thehigh-concentration carrier layer, the series resistance can be reducedgreatly.

The second and third electrodes may include respective pad electrodes,while respective bump electrodes may be arranged on these padelectrodes.

The photodetector device may further comprise a light-reflecting film,provided on the second main face, covering the photodetecting region.Light having passed the multilayer structure without being absorbed isreflected by the light-reflecting film, and then is incident on themultilayer structure again, which increases the quantity of lightabsorbed by the multilayer structure, whereby photosensitivity can beimproved more.

The light-transmitting layer may include a lens part converging theincident light. In this case, the incident light can be convergedefficiently even when the photodetecting region is smaller than theilluminating area of the incident light. The photodetector device inaccordance with the present invention may comprise a plurality ofphotodetecting regions arranged in a row.

Another aspect of the present invention relates to a method ofmanufacturing a semiconductor photodetector device. This methodcomprises the steps of preparing a semiconductor substrate; providing amultilayer structure on the semiconductor substrate, the multilayerstructure including a plurality of compound semiconductor layerslaminated and having first and second main faces opposing each other,the second main face facing the semiconductor substrate; forming aphotodetecting region near the first main face within the multilayerstructure; providing a first electrode electrically connected to thephotodetecting region onto the first main face of the multilayerstructure; forming a light-transmitting layer optically transparent toincident light onto the first main face of the multilayer structure soas to cover the photodetecting region and first electrode; removing thesemiconductor substrate after forming the light-transmitting layer; andforming a second electrode electrically connected to the first electrodeonto the second main face of the multilayer structure while forming athird electrode electrically connected to a part near the second mainface in the multilayer structure onto the second main face afterremoving the semiconductor substrate.

Since the semiconductor substrate is removed after forming thelight-transmitting layer onto the first main face of the multilayerstructure, a semiconductor photodetector device in which thelight-transmitting layer is arranged on the opposite side of the secondand third electrodes for taking out output signals can be manufacturedeasily.

Since the light-transmitting layer remains after removing thesemiconductor substrate, the mechanical strength of the multilayerstructure will be held by the light-transmitting layer even if theplurality of compound semiconductor layers included in the multilayerstructure are made thinner. Unlike the prior art mentioned above, thereis no need to leave a part maintaining the substrate thickness, wherebythe device easily reduces its size. Before forming thelight-transmitting layer, the semiconductor substrate keeps themechanical strength.

The step of forming the light-transmitting layer may include the stepsof forming a film made of silicon oxide so as to cover thephotodetecting region and first electrode; and securing a glasssubstrate optically transparent to the incident light onto the film madeof silicon oxide. Silicon oxide can be fused to glass, and thus can bondthe multilayer structure and glass substrate to each other without usingother adhesives. Therefore, the light incident on the glass substrateside can reach the multilayer structure without being absorbed byadhesives.

The step of forming the light-transmitting layer may include the step offorming a film made of silicon oxide or a resin so as to cover thephotodetecting region and first electrode.

The step of removing the semiconductor substrate may include the step ofremoving the semiconductor substrate by wet etching. The step of formingthe multilayer structure may include the step of forming an etching stoplayer for stopping wet etching between the semiconductor substrate andthe plurality of compound semiconductor layers. Using an etchant whichcan etch the semiconductor substrate but not the etching stop layer canselectively remove the semiconductor substrate. Therefore, thesemiconductor substrate can be removed reliably and easily while leavingthe plurality of compound semiconductor layers.

The method in accordance with the present invention may further comprisethe step of removing the etching stop layer by wet etching afterremoving the semiconductor substrate. Using an etchant which can etchthe etching stop layer but not the compound semiconductor layers canselectively remove the etching stop layer alone. Therefore, the etchingstop layer can be removed reliably and easily while leaving theplurality of compound semiconductor layers.

The plurality of compound semiconductor layers may include ahigh-concentration carrier layer of a first conductive type, alight-absorbing layer of the first conductive type, and a cap layer ofthe first conductive type. The step of forming the multilayer structuremay include the step of successively laminating the high-concentrationcarrier layer, light-absorbing layer, and cap layer on the semiconductorsubstrate. The step of forming the photodetecting region may include thestep of forming a region of a second conductive type including at leasta part of the cap layer as the photodetecting region.

This method may further comprise the steps of forming a depression aboutthe photodetecting region; and providing a wiring electrode forelectrically connecting the first electrode to the second electrode inthe depression. The step of forming the third electrode may include thestep of forming the third electrode such that the third electrode iselectrically connected to a part positioned near the photodetectingregion in the high-concentration carrier layer. The depression formedabout the photodetecting region separates the photodetecting region atleast partly from the other parts of the multilayer structure, and thuscan reduce parasitic capacitance by a greater amount. When the wiringelectrode arranged in the depression is utilized as a through electrodepenetrating through the multilayer structure, the through electrode canbe formed very easily.

The step of forming the second electrode may include the step of forminga through lead penetrating through the multilayer structure, andelectrically connecting the first electrode to the second electrodethrough the through lead. The step of forming the third electrode mayinclude the step of forming the third electrode such that the thirdelectrode is electrically connected to the high-concentration carrierlayer. In this case, the through lead can electrically connect the firstand second electrodes to each other reliably. Also, since the electrodeis directly drawn from the high-concentration carrier layer, the seriesresistance can be reduced greatly.

The method in accordance with the present invention may further comprisethe step of forming a light-reflecting film covering the photodetectingregion onto the second main face of the multilayer structure. In thiscase, light having passed the multilayer structure without beingabsorbed is reflected by the light-reflecting film, and then is incidenton the multilayer structure again, which increases the quantity of lightabsorbed by the multilayer structure, whereby photosensitivity can beimproved.

The light-transmitting layer may include a lens part converging theincident light. In this case, the incident light can be convergedefficiently even when the photodetecting region is smaller than theilluminating area of the incident light.

The present invention will further be understood from the followingdetailed descriptions and attached drawings. The attached drawings aregiven by illustration only, and do not intend to limit the scope of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing the semiconductor photodetectordevice in accordance with a first embodiment.

FIG. 2 is a schematic sectional view taken along the line II-II of FIG.1.

FIG. 3 is a schematic sectional view showing a manufacturing step of thesemiconductor photodetector device in accordance with the firstembodiment.

FIG. 4 is a schematic sectional view showing a manufacturing step of thesemiconductor photodetector device in accordance with the firstembodiment.

FIG. 5 is a schematic sectional view showing a manufacturing step of thesemiconductor photodetector device in accordance with the firstembodiment.

FIG. 6 is a schematic sectional view showing a manufacturing step of thesemiconductor photodetector device in accordance with the firstembodiment.

FIG. 7 is a schematic sectional view showing a manufacturing step of thesemiconductor photodetector device in accordance with the firstembodiment.

FIG. 8 is a schematic sectional view showing a manufacturing step of thesemiconductor photodetector device in accordance with the firstembodiment.

FIG. 9 is a schematic sectional view showing a manufacturing step of thesemiconductor photodetector device in accordance with the firstembodiment.

FIG. 10 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the firstembodiment.

FIG. 11 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the firstembodiment.

FIG. 12 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the firstembodiment.

FIG. 13 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the firstembodiment.

FIG. 14 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the firstembodiment.

FIG. 15 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the firstembodiment.

FIG. 16 is a schematic sectional view showing the semiconductorphotodetector device in accordance with a second embodiment.

FIG. 17 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the secondembodiment.

FIG. 18 is a schematic sectional view showing the semiconductorphotodetector device in accordance with a third embodiment.

FIG. 19 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the thirdembodiment.

FIG. 20 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the thirdembodiment.

FIG. 21 is a schematic sectional view showing the semiconductorphotodetector device in accordance with a fourth embodiment.

FIG. 22 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fourthembodiment.

FIG. 23 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fourthembodiment.

FIG. 24 is a schematic plan view showing the semiconductor photodetectordevice in accordance with a fifth embodiment.

FIG. 25 is a schematic sectional view taken along the line XXV-XXV ofthe semiconductor photodetector device shown in FIG. 24.

FIG. 26 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fifthembodiment.

FIG. 27 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fifthembodiment.

FIG. 28 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fifthembodiment.

FIG. 29 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fifthembodiment.

FIG. 30 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fifthembodiment.

FIG. 31 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fifthembodiment.

FIG. 32 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the fifthembodiment.

FIG. 33 is a schematic sectional view showing the semiconductorphotodetector device in accordance with a sixth embodiment.

FIG. 34 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the sixthembodiment.

FIG. 35 is a schematic sectional view showing the semiconductorphotodetector device in accordance with a seventh embodiment.

FIG. 36 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the seventhembodiment.

FIG. 37 is a schematic sectional view showing a manufacturing step ofthe semiconductor photodetector device in accordance with the seventhembodiment.

FIG. 38 is a schematic sectional view showing the semiconductorphotodetector device in accordance with an eighth embodiment.

FIG. 39 is a schematic sectional view of the semiconductor photodetectordevice array in accordance with an embodiment.

FIG. 40 is a schematic sectional view of the semiconductor photodetectordevice array in accordance with an embodiment.

FIG. 41 is a schematic sectional view showing the structure of theoptical interconnection system in accordance with an embodiment.

EXPLANATIONS OF NUMERALS OR LETTERS

1: glass substrate; 121 a: lens part; 2: etching stop layer; 3 (3 a):high-concentration carrier layer; 5 (5 a): light-absorbing layer; 7 (7a): cap layer; 9: photodetecting region; 10: film; 11: photodetectingpart; 12: depression; 17: contact electrode; 21: first electrode; 23:contact electrode; 25: first wiring electrode; 27: first pad electrode(second electrode); 31: third electrode; 33: second pad electrode; 35:second wiring electrode; 41: bump electrode; 51: semiconductorsubstrate; 60: film; 131 a: lens part; 71: contact electrode; 73:through lead; 81: third electrode; 83: contact electrode; LS1, LS2:layer structure; PD1 to PD8: semiconductor photodetector device; PDA1,PDA2: semiconductor photodetector array.

BEST MODES FOR CARRYING OUT THE INVENTION

Semiconductor photodetector devices in accordance with embodiments ofthe present invention will be explained with reference to the drawings.In the explanation, the same numerals will be used for the sameconstituents or those having the same functions without repeating theiroverlapping descriptions.

FIRST EMBODIMENT

FIG. 1 is a schematic plan view showing the semiconductor photodetectordevice in accordance with a first embodiment. FIG. 2 is a schematicsectional view taken along the line II-II of FIG. 1. FIG. 1 does notdepict bump electrodes 41.

A semiconductor photodetector device PD1 comprises a multilayerstructure LS1 and a glass substrate 1. The glass substrate 1 has twomain faces opposing each other, i.e., front face 121 and rear face 122.The multilayer structure LS1 is provided on the rear face 122 of theglass substrate 1. This semiconductor photodetector device PD1 is aphotodetector device of front-illuminated type in which light isincident on the multilayer structure LS1 from the glass substrate 1side. The semiconductor photodetector device PD1 is a photodetectordevice for short-distance optical communications in the wavelength bandof 0.85 μm, for example.

The multilayer structure LS1 includes an etching stop layer 2, an n-type(first conductive type) high-concentration carrier layer 3, an n-typelight-absorbing layer 5, and an n-type cap layer 7. The multilayerstructure LS1 has two main faces opposing each other, i.e., front face101 and rear face 102. A passivation film 19 which will be explainedlater is formed on the front face 101, whereas an electricallyinsulating film (passivation film) 20 is formed on the rear face 102.The electrically insulating film 20 is made of SiN_(X) and has athickness of about 0.2 μm, for example.

The multilayer structure LS1 has a photodetecting part 11 and adepression 12 surrounding the photodetecting part 11. The photodetectingpart 11 includes an n-type high-concentration carrier layer 3 a, ann-type light-absorbing layer 5 a, and an n-type cap layer 7 a, and has amesa form (a truncated cone form in this embodiment). The photodetectingpart 11 has a p-type (second conductive type) photodetecting region 9.The photodetecting region 9 includes at least a part of the cap layer 7a. In this embodiment, the cap layer 7 a and light-absorbing layer 5 arepartly included in the photodetecting region 9. The top part of thephotodetecting part 11 and the photodetecting region 9 are circular asseen in the direction along which light is incident.

At the top part of the photodetecting part 11, a depression 13 is formedon the outside of photodetecting region 9 as seen in the direction alongwhich light is incident. The depression 13 is formed like a groove suchas to reach the high-concentration carrier layer 3 a and surround thephotodetecting region 9. Thus, the photodetecting part 11 includes amesa-like inner part 11 a containing the photodetecting region 9 and anouter part 11 b surrounding the inner part 11 a. The depression 13 isformed like letter C extending along the edge of the photodetectingregion 9 while leaving a portion of the top part of the photodetectingpart 11 as seen in the direction along which light is incident.

A contact electrode 17 is arranged on the bottom part of the depression13. The contact electrode 17 is electrically connected to thehigh-concentration carrier layer 3 a. The contact layer 17 is made of amultilayer body of Au-Ge/Ni/Au, and has a thickness of about 1000 mn. Aswith the depression 13, the contact electrode 17 is formed like letter Cas seen in the direction along which light is incident.

On the front face of the photodetecting part 11, i.e., front face 101 ofthe multilayer structure LS1, the passivation film 19 is formed so as tocover the photodetecting region 9. The passivation film 19 is made ofSiN_(X), for example. In this embodiment, the passivation film 19functions as an antireflection film. Therefore, the thickness of thepassivation film 19 is set to λ/(4n), where n is the refractive index ofthe passivation film 19, and λ is the received light wavelength. In thecase of a photodetector device for short-distance optical communicationsin the wavelength band of 0.85 μm, for example, the thickness of thepassivation film 19 is 1000 to 3000 Å. An antireflection film may beformed separately from the passivation film 19 so as to cover thephotodetecting region 9.

The high-concentration carrier layers 3 and 3 a are compoundsemiconductor layers and are made of AlGaAs (where Al composition is0.3) having a carrier concentration of about 1×10¹⁸/cm³. Thehigh-concentration carrier layers 3 and 3 a have a thickness of about 2μm.

The light-absorbing layers 5 and 5 a are compound semiconductor layersand are made of GaAs having a carrier concentration of about 1×10¹⁴/cm³,for example. The light-absorbing layers 5 and 5 a have a thickness ofabout 3 μm.

The cap layers 7 and 7 a are compound semiconductor layers and are madeof AlGaAs (where Al composition ratio is 0.3) having a carrierconcentration of about 5×10¹⁵/cm³, for example. The cap layers 7 and 7 ahave a thickness of about 0.3 μm. The Al composition ratio in the caplayers 7 and 7 a is preferably 0.3 or greater. Though the Al compositionratio x of 0.04 is sufficient for detecting light having a wavelength of0.85 μm or longer, it will be more preferred if the Al composition ratiois 0.3 or greater. However, the Al composition ratio of the cap layers 7and 7 a can be determined as appropriate according to the wavelength oflight to be detected. For detecting short-wavelength light having awavelength of 0.65 μm, for example, the Al composition ratio of 0.4 orgreater is necessary.

The photodetecting region 9 is provided on the front face 101 of themultilayer structure LS1. The photodetecting region 9 is formed bythermally diffusing p-type impurities (e.g., Zn) into a desirable areaof the cap layer 7 a and inverting this area into p-type. Thephotodetecting region 9 has a depth of about 0.4 μm and a diameter of 5to 200 μm. The depression (groove) 13 has a width of about 5 μm. Thediameter of received light depends on a property required for thephotodetector device and can be designed within a broad range of 1 μm to10 mm.

A first electrode 21 is arranged on the front face 101 of the multilayerstructure LS1. The first electrode 21 includes a contact electrode 23and an electrode part 25 a which will be explained later. The contactelectrode 23 is formed like a ring on the front face of thephotodetecting region 9, and is electrically connected to thephotodetecting region 9. The contact electrode 23 is made of Ti/Pt/Au,and has a thickness of about 1000 nm. The contact layer 23 is arrangedso as to be buried in the photodetecting region 9 in the cap layer 7 ain FIG. 2, but may be arranged on the cap layer 7 a and photodetectingregion 9 as well.

A first wiring electrode 25 is electrically connected to the contactelectrode 23. The first wiring electrode 25 partly covers thephotodetecting part 11 and depression 12, and is arranged on thepassivation film 19. The first wiring electrode 25 comprises anelectrode part 25 a arranged on the top part of the photodetecting part11 and an electrode part 25 b arranged within the depression 12. Thefirst wiring electrode 25 is made of Ti/Pt/Au, and has a thickness ofabout 1.5 μm. The electrode part 25 a positioned on the photodetectingpart 11 is arranged on the contact electrode 23 such as to expose atleast a part of the photodetecting region 9, and is shaped like a ring.The electrode part 25 a is connected to the contact electrode 23 througha contact hole 19 a formed in the passivation film 19.

As a second electrode, a first pad electrode 27 is arranged on the rearface 102 of the multilayer structure LS1. The first pad electrode 27 ismade of Ti/Pt/Au, and has a thickness of about 1.5 μm. The first padelectrode 27 is electrically connected to the first wiring electrode 25(electrode part 25 b) through a contact hole 29 penetrating through theelectrically insulating film 20, etching stop layer 2, and passivationfilm 19. As a result, the contact electrode 23 is electrically connectedto the first pad electrode 27 through the first wiring electrode 25. Abump electrode 41 is arranged on the first pad electrode 27.

A third electrode 31 is arranged on the rear face 102 of the multilayerstructure LS1. The third electrode 31 includes a second pad electrode 33and a second wiring electrode 35. The second pad electrode 33 and secondwiring electrode 35 are made of Ti/Pt/Au, and have a thickness of about1.5 μm. The second pad electrode 33 is electrically connected to thehigh-concentration carrier layer 3 a and contact electrode 17 through acontact hole 37 penetrating through the electrically insulating film 20,etching stop layer 2, and high-concentration carrier layer 3. The secondwiring electrode 35 is formed below the rear face of the photodetectingregion 9 such as to cover this rear face, and functions as alight-reflecting film. A light-reflecting film may be formed below thephotodetecting region 9 separately from the second wiring electrode 35.A bump electrode 41 is arranged on the second pad electrode 33 as in thefirst pad electrode 27.

The taking out of electrodes from the photodetecting region 9 isrealized by the contact electrode 23, first wiring electrode 25, firstpad electrode 27, and bump electrode 41. The taking out of electrodesfrom the high-concentration carrier layer 3 a is realized by the contactelectrode 17, second pad electrode 33, and bump electrode 41.

A film 10 is formed on the front face 101 of the multilayer structureLS1 so as to cover the photodetecting region 9 and first electrode 21(the contact electrode 23 and the electrode part 25 a of the firstwiring electrode 25). The film 10 is made of silicon oxide (SiO₂) and isoptically transparent to incident light. The surface 10 a on the sideopposite from the multilayer structure LS1 in the film 10 is flattened.The film 10 has a thickness of 3 to 10 μm.

The glass substrate 1 is in contact with and attached to the surface 10a of the film 10. The glass substrate 1 has a thickness of about 0.3 mmand is optically transparent to incident light.

In the following, a method of manufacturing the semiconductorphotodetector device PD1 will be explained with reference to FIGS. 3 to15. FIGS. 3 to 15 are views for explaining this manufacturing method,and show a vertical section of the semiconductor photodetector devicePD1. This manufacturing method successively executes the following steps(1) to (13):

Step (1)

First, a semiconductor substrate 51 is prepared. The semiconductorsubstrate 51 has a thickness of 300 to 500 μm and is made of n-type GaAshaving a carrier concentration of about 1×10¹⁸/cm³, for example. Abuffer layer 53 and an etching stop layer 2 are successively grown onone main face (front face) 111 of the semiconductor substrate 51 byhydride vapor-phase growth, chloride vapor-phase growth, metal-organicchemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or thelike, so as to be laminated (see FIG. 3). Thereafter, an n-typehigh-concentration carrier layer 3, an n-type light-absorbing layer 5,and an n-type cap layer 7 are successively grown on the etching stoplayer 2 by hydride vapor-phase growth, chloride vapor-phase growth,MOCVD, MBE, or the like, so as to be laminated (see FIG. 3).

The buffer layer 53 is made of nondoped GaAs and has a thickness ofabout 0.05 μm. The etching stop layer 2 is made of nondoped AlGaAs(having an Al composition of 0.5) and has a thickness of about 1.0 μm.The etching stop layer 2 is formed so as to be positioned between thesemiconductor substrate 51 and high-concentration carrier layer 3. Itwill be preferred if the etching stop layer 2 has an Al compositionratio of 0.4 or greater. This is because AlGaAs having an Al compositionratio of 0.4 or greater is harder to be etched by an etchant used whenetching GaAs which will be explained later.

The foregoing step (1) forms the multilayer structure LS1 and bufferlayer 53 on the front face 111 of the semiconductor substrate 51.

Step (2)

Next, a film made of SiO₂ or SiN_(X) is formed on the cap layer 7. Then,the film 55 is patterned, so as to provide an opening 55 a at a positionto form a photodetecting region 9 (see FIG. 4). Thereafter, using thepatterned film 55 as a mask, impurities (e.g., Zn) are thermallydiffused into the cap layer 7, so as to invert the conductive type of aportion of the cap layer 7 into p-type. Thus, the photodetecting region9 is formed near the front face 101 remote from the semiconductorsubstrate 51 within the multilayer structure LS1 (see FIG. 4).Thereafter, the film 55 is removed by buffered hydrofluoric acid (BHF).

Step (3)

Next, a resist film 56 having an opening 56 a at a position to form adepression 13 is formed on the cap layer 7. The resist film 56 can beformed by using photolithography. Then, using the resist film 56 as amask, etching (wet etching) is performed with a mixed liquid of Br₂ andmethanol until the high-concentration carrier layer 3 is exposed. Thisforms the depression 13 (see FIG. 5). Subsequently, the resist film 56is removed.

Step (4)

Next, a resist film 57 having an opening 57 a at a position to form adepression 12 is formed on the cap layer 7. The resist film 57 can beformed by using photolithography. Then, using the resist film 57 as amask, etching (wet etching) is performed with a mixed liquid of Br₂ andmethanol until the etching stop layer 2 is exposed, so as to form thedepression 12. This forms a photodetecting part 11 in a mesa form (seeFIG. 6). Namely, the photodetecting part 11 includes thehigh-concentration carrier layer 3 a, light-absorbing layer 5 a, and caplayer 7 a. Here, arranging the resist film 57 over the outer part 11 bcan appropriately regulate the advancing of etching not only in thedepth direction but also in lateral directions, which makes it possibleto form the depression 13 and photodetecting part 11 properly. As aresult, the yield at the time of manufacturing the semiconductorphotodetector device PD1 can be made higher. Thereafter, the resist film57 is removed.

Step (5)

Next, a resist film (not depicted) having an opening at a positioncorresponding to the depression 13 is formed. Then, on thehigh-concentration carrier layer 3 (3 a) exposed by forming thedepression 13, a contact electrode 17 made of Au-Ge/Ni/Au is formed byvapor deposition using this resist film as a mask and liftoff (see FIG.7). Also, a resist film is formed again such as to have an opening at aposition to form a contact electrode 23, and the contact electrode 23made of Ti/Pt/Au is formed in the photodetecting region 9 by vapordeposition and liftoff while using this resist film as a mask (see FIG.7). Subsequently, the resist film is removed. The contact electrode 23is formed so as to be buried in the photodetecting region 9 in the caplayer 7 a in FIG. 7, but may be formed on the front face of the caplayer 7 a and photodetecting region 9 as well.

Step (6)

Next, a passivation film 19 made of SiN_(X) is formed on the front face101 of the multilayer structure LS1 by PCVD. Then, a resist film (notdepicted) having openings positioned above the contact electrodes 17, 23is formed, and a contact hole 19 a is formed in the passivation film 19(see FIG. 8). Subsequently, the resist film is removed.

Step (7)

Next, a resist film (not depicted) having an opening at a positioncorresponding to a first wiring electrode 25 is formed. Then, using thisresist film as a mask, the first wiring electrode 25 made of Ti/Pt/Au isformed by liftoff (see FIG. 9). The above-mentioned steps (6) and (7)form a first electrode 21 on the front face 101 side of the multilayerstructure LS1. Subsequently, the resist film is removed. Thereafter,sintering is performed in an H₂ atmosphere.

Step (8)

Next, a film 10 is formed and flattened oh the front face 101 of themultilayer structure LS1 so as to cover the photodetecting region 9 andfirst electrode 21 (see FIG. 10). Here, the surface 10 a positioned onthe side opposite from the multilayer structure LS1 in the film 10 isflattened as a front face of a structure including the multilayerstructure LS1 and semiconductor substrate 51. The film 10 can be formedby plasma chemical vapor deposition or coating. Here, “flattened” doesnot always mean that there are no irregularities at all. Slightirregularities may exist as long as a glass substrate 1 and the film 10can be fused to each other while a surface of the glass substrate 1 andthe surface 10 a of the film 10 are in contact with each other when theglass substrate 1 and the semiconductor substrate 51 are pressed andheated while being stacked together with the film 10 interposedtherebetween in step (9) which will be explained later.

Step (9)

Next, the glass substrate 1 is attached to the semiconductor 51 formedwith the multilayer structure LS1, buffer layer 53, and film 10 (seeFIG. 11). First, the glass substrate 1 is prepared, and one main face(rear face) 122 of the glass substrate 1 is cleaned. Then, the glasssubstrate 1 and the semiconductor substrate 51 are stacked such that thecleaned rear face 122 of the glass substrate 1 and the surface 10 a ofthe film 10 are in contact with each other. Subsequently, the stackedglass substrate 1 and semiconductor substrate 51 are pressed and heated,so as to attach the glass substrate 1 and film 10 to each other byfusion.

Specifically, it will be preferred if the pressure applied to thestacked glass substrate 1 and semiconductor substrate 51 is about 98 kPawhile the heating temperature is 500 to 700° C. Since the uppermost film10 on the semiconductor substrate 51 is made of silicon oxide, thepressing and heating under such a condition fuses the surface 10 a ofthe film 10 to the rear face 122 of the glass substrate 1, therebysecuring the multilayer structure LS1 and semiconductor substrate 51 tothe glass substrate 1.

For performing this attaching step, it is desirable that not only therear face 122 of the glass substrate 1 but also the surface 10 a of thefilm 10 be clean. To this aim, it will be preferred if a contrivance ismade such as to perform the fusing operation immediately after takingout the semiconductor substrate 51 from the PCVD apparatus used forforming the film 10, for example.

Preferably, the glass substrate employed has a coefficient of thermalexpansion close to that of GaAs. This can minimize the stress occurringbetween the semiconductor substrate 51 and glass substrate 1 because ofthe difference between their coefficients of thermal expansion in thecooling step after heating, and thus can suppress the decrease ofbonding strength and occurrence of crystal defects due to the stress tothe minimum.

Step (10)

Next, the semiconductor substrate 51 is removed. After the multilayerstructure LS1 and semiconductor substrate 51 are secured to the glasssubstrate 1, the main face positioned on the side opposite from theglass substrate 1 in the semiconductor substrate 51, i.e., the rear face112, is exposed. In this step, etching is performed from the rear face112 side of the semiconductor substrate 51, so as to remove thesemiconductor substrate 51 and buffer layer 53 (see FIG. 12).

Specifically, an etchant exhibiting a lower etching rate to the etchingstop layer 2 is used, so as to remove the semiconductor substrate 51 andbuffer layer 53. This yields the glass substrate 1 mounted with themultilayer structure LS1. Preferably used as the etchant is a mixedsolution (NH₄OH:H₂O₂=1:5) of aqueous ammonia (NH₄OH) and aqueoushydrogen peroxide (H₂O₂). First, the glass substrate 1 and semiconductorsubstrate 51 attached together are dipped into the mixed solution ofNH₄OH and H₂O₂. This etches the semiconductor substrate 51 from the rearside. When the etching advances to such an extent that the semiconductorsubstrate 51 and buffer layer 53 are removed, the etching stop layer 2is exposed in the etchant. The etching stop layer 2 (Al_(0.5)Ga_(0.5)As)has a high tolerance to this etchant, whereby its etching rate becomesvery low. Therefore, the etching automatically stops at the time whenthe etching stop layer 2 is exposed. Thus, the semiconductor substrate51 and buffer layer 53 are removed. The semiconductor substrate 51 andbuffer layer 53 may also be removed by chemical mechanical polishing(CMP) instead of etching.

Step (11)

Next, an electrically insulating film 20 made of SiN_(X) is formed onthe rear face 102 of the etching stop layer 2 by PCVD (see FIG. 13).

Step (12)

Next, a resist film (not depicted) having an opening at a position toform a contact hole 37 is formed on the electrically insulating film 20.Using this resist film as a mask, the electrically insulating film 20,etching stop layer 2, and high-concentration carrier layer 3 are etched(wet-etched) until the contact electrode 17 is exposed. This forms thecontact hole 37 (see FIG. 14). Preferably employed as etchants arebuffered hydrofluoric acid (BHF) for the electrically insulating film20, hydrochloric acid (HCl) for the etching stop layer 2, and a mixedsolution (NH₄OH:H₂O₂=1:5) of aqueous ammonia (NH₄OH) and aqueoushydrogen peroxide (H₂O₂) for the high-concentration carrier layer 3.Subsequently, the resist film is removed.

Next, a resist film (not depicted) having an opening at a position toform a contact hole 29 is formed on the electrically insulating film 20.Using this resist film as a mask, the electrically insulating film 20,etching stop layer 2, and passivation film 19 are etched (wet-etched)until the first wiring electrode 25 (electrode part 25 b) is exposed.This forms the contact hole 29 (see FIG. 14). Preferably employed asetchants are buffered hydrofluoric acid (BHF) for the electricallyinsulating film 20, and hydrochloric acid (HCl) for the passivation film19. Subsequently, the resist film is removed.

Step (13)

Next, a resist film (not depicted) having openings at respectivepositions corresponding to a first pad electrode 27, a second padelectrode 33, and a second wiring electrode 35 is formed. Then, usingthis resist film as a mask, the first pad electrode 27, second padelectrode 33, and second wiring electrode 35 made of Ti/Pt/Au are formedby liftoff (see FIG. 15). At this time, the second wiring electrode 35is formed so as to cover the rear face (the surface on the side oppositefrom the light-incident surface) of the photodetecting region 9. Here,the second pad electrode 33 and second wiring electrode 35 are formedintegrally with each other. Subsequently, the resist film is removed.Thereafter, sintering is performed in an H₂ atmosphere. Though thesecond pad electrode 33 and second wiring electrode 35 are formedintegrally with each other, they may be formed separately from eachother as well.

These steps (1) to (13) complete the semiconductor photodetector devicePD1 having the structure shown in FIGS. 1 and 2.

The bump electrodes 41 can be obtained by forming solder on the firstpad electrode (second electrode) 27 and second pad electrode 33 byplating, solder ball mounting, or printing, and then performing reflow.The bump electrodes 41 are not limited to solder, but may be gold bumps,nickel bumps, copper bumps, or conductive resin bumps containing a metalsuch as conductive filler.

In this embodiment, the mechanical strength of the multilayer structureLS1 (high-concentration carrier layer 3, light-absorbing layer 5, caplayer 7, etc.) is held by the glass substrate 1 and film 10 even whenthe high-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7 are made thinner. Unlike the conventional semiconductorphotodetector devices, there is no need to form a part maintaining thesubstrate thickness, which makes it easier to reduce the size of thesemiconductor photodetector device PD1.

Since the first pad electrode 27 and third electrode 31 (the second padelectrode 33 and second wiring electrode 35) for taking out outputsignals are arranged on the rear face 102 of the multilayer structureLS1, the semiconductor photodetector device PD1 can be mounted while therear face 102 (the main face on the side opposite from the front face101 arranged with the photodetecting region 9) opposes a mountingsurface of an external substrate or the like. Therefore, thesemiconductor photodetector device PD1 can be mounted easily.

Since the multilayer structure LS1 is secured to the glass substrate 1by way of the film 10, the glass substrate 1 can be attached to themultilayer structure LS1 without using other adhesives. As with theglass substrate 1, silicon oxide constituting the film 10 is opticallytransparent to light to be detected. Therefore, the incident lighttransmitted through the glass substrate 1 can reach the multilayerstructure LS1 (photodetecting region 9) without being absorbed byadhesives. This can prevent the sensitivity of photodetection fromdecreasing.

The photodetecting part 11 has a mesa structure including thehigh-concentration carrier layer 3 a, light-absorbing layer 5 a, caplayer 7 a, and photodetecting region 9, thereby being separated from itssurrounding semiconductor layers. This can further reduce the parasiticcapacitance.

The first electrode 21 (the contact electrode 23 and the electrode part25 a of the first wiring electrode 25) is electrically connected to thefirst pad electrode (second electrode) 27 through the electrode part 25b of the first wiring electrode 25 positioned within the depression 12formed such as to surround the photodetecting part 11. The thirdelectrode 31 (the second pad electrode 33 and second wiring electrode35) is electrically connected to the high-concentration carrier layerpart 3 a included in the photodetecting part 11. Consequently, theelectrode part 25 b in the depression 12 can be utilized as a part of athrough electrode penetrating through the multilayer structure LS1,whereby the through electrode can be formed very easily. Using wetetching as a technique for forming the contact hole 29 can manufacturethe semiconductor photodetector device PD1 at low cost with a favorableyield.

Since the electrode is directly drawn from the high-concentrationcarrier layer 3 a of the photodetecting part 11, the series resistancecan be reduced greatly in this embodiment.

The second wiring electrode 35 covering the photodetecting region 9 isformed on the rear face 102 of the multilayer structure LS1. Therefore,light having passed the light-absorbing layer 5 a without being absorbedis reflected by the second wiring electrode 35, and then is incident onthe light-absorbing layer 5 a again and absorbed thereby, wherebyphotosensitivity can further be improved.

In the manufacturing method in accordance with this embodiment, the film10 covering the photodetecting region 9 and first electrode 21 is formedon the front face 101 of the multilayer structure LS1, the glasssubstrate 1 is attached to the film 10 such that the surface 10 a of thefilm 10 is in contact with the rear face 122 of the glass substrate 1,and then the semiconductor substrate 51 is removed. This can easilymanufacture the semiconductor photodetector device PD1 having astructure in which the glass substrate 1 is attached onto the front face101 of the multilayer structure LS1 through the film 10.

Since the glass substrate 1 and film 10 remain after removing thesemiconductor substrate 51, the mechanical strength of the multilayerstructure LS1 is held by the glass substrate 1 and film 10 in subsequentmanufacturing steps. Before attaching the glass substrate 1, thesemiconductor substrate 51 keeps the mechanical strength of themultilayer structure LS1.

In the step of forming the multilayer structure LS1, the etching stoplayer 2 for stopping wet etching is formed between the semiconductorsubstrate 51 and high-concentration carrier layer 3. Therefore, usingetchants which cannot etch the etching stop layer 2 can selectivelyremove the semiconductor substrate 51. Consequently, the semiconductorsubstrate 51 can be removed reliably and easily while leaving thehigh-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7.

SECOND EMBODIMENT

FIG. 16 is a schematic sectional view showing the structure of thesemiconductor photodetector device in accordance with a secondembodiment. This semiconductor photodetector device PD2 differs from thesemiconductor photodetector device PD1 in accordance with the firstembodiment in that the glass substrate 1 is formed with a lens part 121a.

The semiconductor photodetector device PD2 comprises a multilayerstructure LS1 and the glass substrate 1. This semiconductorphotodetector device PD2 is a photodetector device of front-illuminatedtype in which light is incident on the multilayer structure LS1 from theglass substrate 1 side. The semiconductor photodetector device PD2 is aphotodetector device for short-distance optical communications in thewavelength band of 0.85 μm, for example.

The lens part 121 a converging incident light is formed on the frontface 121 of the glass substrate 1. The other part 121 b of the frontface 121 is thicker than the lens part 121 a. Namely, the lens part 121a is depressed from the thickest part 121 b of the front face 121.

Next, a method of manufacturing the semiconductor photodetector devicePD2 will be explained with reference to FIG. 17. FIG. 17 is a view forexplaining this manufacturing method, and shows a vertical section ofthe semiconductor photodetector device PD2.

This manufacturing method successively executes the following steps (1)to (13). Steps (1) to (8) are the same as steps (1) to (8) in the firstembodiment, and thus will not be explained.

Step (9)

Next, the glass substrate 1 is attached to the semiconductor substrate51 formed with the multilayer structure LS1, buffer layer 53, and film10 (see FIG. 17). The attaching method is the same as that in step (9)in the first embodiment. Specifically, the glass substrate 1 having thefront face 121 formed with the lens part 121 a is prepared, and the rearface 122 of the glass substrate 1 is cleaned. Then, the glass substrate1 and the semiconductor substrate 51 are stacked together such that thecleaned rear face 122 and the surface 10 a remote from the multilayerstructure LS1 in the film 10 are in contact with each other.Subsequently, the stacked glass substrate 1 and semiconductor substrate51 are pressed and heated, so that the glass substrate 1 and film 10 areattached together by fusion. Details of this attaching method are thesame as those in step (9) in the first embodiment.

The alignment between the photodetecting region 9 on the semiconductorsubstrate 51 and the lens part 121 a on the glass substrate 1 can easilybe effected with reference to a marker provided on the rear face 122side of the glass substrate 1 by providing the marker and using adouble-sided aligner. Instead of providing the marker, the outer shapeof the lens part 121 a may be utilized as a marker.

Steps (10) to (13) are the same as steps (10) to (13) in the firstembodiment, and thus will not be explained here. These steps (1) to (13)complete the semiconductor photodetector device PD2 having the structureshown in FIG. 16.

In this embodiment, as in the above-mentioned first embodiment, themechanical strength of the multilayer structure LS1 (laminatedhigh-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7) is held by the glass substrate 1 and film 10, while thesemiconductor photodetector device PD2 is easily made smaller. Also, thesemiconductor photodetector device PD2 can be mounted easily.

Since the glass substrate 1 is provided with the lens part 121 a, theincident light can be received efficiently even when the photodetectingregion 9 is smaller than the illuminating area of the incident light. Asa result, the semiconductor photodetector device PD2 with an excellentS/N ratio and high reliability can be obtained.

In this embodiment, the lens part 121 a is formed as being depressedfrom the thickest part 121 b in the front face 121 of the glasssubstrate 1. Therefore, the glass substrate 1 formed with the lens part121 a can easily be attached to the multilayer structure LS1. Since thelens part 121 a can be processed before being attached, the processingmethod is less likely to be limited, whereby a higher degree of freedomis attained in terms of lens designing such as lens forms.

The lens part 121 a may be formed after attaching the glass substrate 1to the semiconductor substrate 51 mounted with the multilayer structureLS1 and film 10. When the degree of freedom in lens designing isconcerned, however, it will be preferred if the glass substrate 1 havingthe lens part 121 a formed beforehand therewith is attached to thesemiconductor substrate 51.

THIRD EMBODIMENT

FIG. 18 is a schematic sectional view showing the structure of thesemiconductor photodetector device in accordance with a thirdembodiment. This semiconductor photodetector device PD3 differs from thesemiconductor photodetector device PD1 in accordance with the firstembodiment in that it has a film made of silicon oxide (SiO₂) or a resininstead of the glass substrate 1 and film 10.

The semiconductor photodetector device PD3 comprises the multilayerstructure LS1 and a film 60. The film 60 has two main faces opposingeach other, i.e., front face 131 and rear face 132. The multilayerstructure LS1 is provided on the rear face 132 of the film 60. Thissemiconductor photodetector device PD3 is a photodetector device offront-illuminated type in which light is incident on the multilayerstructure LS1 from the film 60 side. The semiconductor photodetectordevice PD3 is a photodetector device for short-distance opticalcommunications in the wavelength band of 0.85 μm, for example.

On the front face 101 of the multilayer structure LS1, the film 60 isformed such as to cover the photodetecting region 9 and the firstelectrode 21 (the contact electrode 23 and the electrode part 25 a ofthe first wiring electrode 25). The film 60 is made of silicon oxide ora resin (e.g., polyimide resin, PMMA, or epoxy resin). The film 60 has athickness of about 50 μm and is optically transparent to incident light.

A method of manufacturing the semiconductor photodetector device PD3will now be explained with reference to FIGS. 19 and 20. FIGS. 19 and 20are views for explaining this manufacturing method, and show a verticalsection of the semiconductor photodetector device PD3.

This manufacturing method successively executes the following steps (1)to (12). Steps (1) to (7) are the same as steps (1) to (7) in the firstembodiment, and thus will not be explained.

Step (8)

Next, the film 60 is formed on the front face 101 side of the multilayerstructure LS1 such as to cover the photodetecting region 9 and firstelectrode 21 (see FIG. 19). When the film 60 is made of silicon oxide,PCVD employing TEOS (Tetraethylorthosilicate) as a film-forming gas forforming a silicon oxide film (SiO₂) can be used for forming the film 60,for example. When the film 60 is made of a resin, on the other hand,coating can be used for forming the film 60, for example.

Step (9)

Next, the semiconductor substrate 51 is removed. After forming the film60, the rear face 112 positioned on the side opposite from the film 60in the semiconductor substrate 51 is exposed. In this step, thesemiconductor substrate 51 and buffer layer 53 are removed by etchingfrom the rear face 112 side of the semiconductor substrate 51 (see FIG.20). The method of etching the semiconductor substrate 51 and bufferlayer 53 is the same as the etching method in step (10) in the firstembodiment.

Steps (10) to (12) are the same as steps (11) to (13) in the firstembodiment, and thus will not be explained here. These steps (1) to (12)complete the semiconductor photodetector device PD3 having the structureshown in FIG. 18.

In this embodiment, as in the above-mentioned first embodiment, themechanical strength of the multilayer structure LS1 (laminatedhigh-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7) is held by the film 60, while the semiconductor photodetectordevice PD3 is easily made smaller. Also, the semiconductor photodetectordevice PD3 can be mounted easily.

FOURTH EMBODIMENT

FIG. 21 is a schematic sectional view showing the structure of thesemiconductor photodetector device in accordance with a fourthembodiment. This semiconductor photodetector device PD4 differs from thesemiconductor photodetector device PD3 in accordance with the thirdembodiment in that the film 60 is formed with a lens part 131 a.

The semiconductor photodetector device PD4 comprises the multilayerstructure LS1 and the film 60. This semiconductor photodetector devicePD4 is a photodetector device of front-illuminated type in which lightis incident on the multilayer structure LS1 from the film 60 side. Thesemiconductor photodetector device PD4 is a photodetector device forshort-distance optical communications in the wavelength band of 0.85 μm,for example.

The front face 131 of the film 60 is formed with the lens part 131 aconverging incident light. The lens part 131 a can be formed by wetetching. For example, as shown in FIG. 22, a resist film 63 having anopening 63 a at a desirable position is formed on the front face 131 ofthe film 60. Then, as shown in FIG. 23, the film 60 is wet-etched whileusing the resist film 63 as a mask. Since etching proceeds isotropicallyin the wet etching, the lens part 131 having a lens effect is formedwhen the opening 63 a of the resist film 63 and the photodetectingregion 9 are appropriately aligned to each other.

In this embodiment, as in the above-mentioned first embodiment, themechanical strength of the multilayer structure LS1 (laminatedhigh-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7) is held by the film 60, while the semiconductor photodetectordevice PD4 is easily made smaller. Also, the semiconductor photodetectordevice PD4 can be mounted easily.

Since the film 60 is provided with the lens part 131 a, the incidentlight can be received efficiently even when the photodetecting region 9is smaller than the illuminating area of the incident light. As aresult, the semiconductor photodetector device PD4 with an excellent S/Nratio and high reliability can be obtained.

FIFTH EMBODIMENT

FIG. 24 is a schematic plan view showing the semiconductor photodetectordevice in accordance with a fifth embodiment. FIG. 25 is a schematicsectional view taken along the line XXV-XXV of FIG. 24. FIG. 24 does notdepict bump electrodes 41.

A semiconductor photodetector device PD5 comprises a multilayerstructure LS2 and a glass substrate 1. The multilayer structure LS2 isprovided on the rear face 122 of the glass substrate 1. Thissemiconductor photodetector device PD5 is a photodetector device offront-illuminated type in which light is incident on the multilayerstructure LS2 from the glass substrate 1 side. The semiconductorphotodetector device PD5 is a photodetector device for short-distanceoptical communications in the wavelength band of 0.85 μm, for example.

The multilayer structure LS2 includes an n-type (first conductive type)high-concentration carrier layer 3, an n-type light-absorbing layer 5,and an n-type cap layer 7. The multilayer structure LS2 has two mainfaces opposing each other, i.e., front face 103 and rear face 104. Thecap layer 7 a is formed with a p-type (second conductive type)photodetecting region 9. A passivation film 19 is formed on the frontface 103 of the multilayer structure LS2. An electrically insulatingfilm 20 is formed on the rear face 104 of the multilayer structure LS2.

On the front face 103 of the multilayer structure LS2, a contactelectrode 71 as a first electrode is arranged on the passivation film19. The contact electrode 71 passes through a contact hole 19 a formedin the passivation film 19, so as to be electrically connected to thephotodetecting region 9. The contact electrode 71 is made of Ti/Pt/Auand has a thickness of about 1.5 μm.

The multilayer structure LS2 is formed with a through hole TH extendingfrom the front face 103 to the rear face 104. The electricallyinsulating film 20 also extends onto the wall face of the multilayerstructure LS2 defining the through hole TH. A through lead 73 isprovided inside of the electrically insulating film 20 within thethrough hole TH. One end part 73 a of the through lead 73 passes througha contact hole 20 a formed in the electrically insulating film 20, so asto be electrically connected to the contact electrode 71.

A first pad electrode 27 (second electrode) and a third electrode 81 arearranged on the rear face 104 of the multilayer structure LS2. The firstpad electrode 27 is formed such as to cover the through lead 73, and iselectrically connected to an end part 73 b on the side opposite from theend part 73 a in the through lead 73. A bump electrode 41 is arranged onthe first pad electrode 27. The taking out of electrodes from thephotodetecting region 9 is realized by the contact electrode 71, throughlead 73, first pad electrode 27, and bump electrode 41.

The third electrode 81 includes a contact electrode 83, a second padelectrode 33, and a second wiring electrode 35. The contact electrode 83passes through a contact hole 20 b formed in the electrically insulatingfilm 20, so as to be electrically connected to the high-concentrationcarrier layer 3. The second pad electrode 33 and second wiring electrode35 are formed so as to cover the contact electrode 83, and areelectrically connected to the contact electrode 83. A bump electrode 41is arranged on the second pad electrode 33 as in the first pad electrode27. The taking out of electrodes from the high-concentration carrierlayer 3 is realized by the contact electrode 83, second pad electrode33, and bump electrode 41.

The second wiring electrode 35 is formed below the rear face of thephotodetecting region 9 such as to cover this rear face, and functionsas a light-reflecting film. A light-reflecting film may be formed belowthe photodetecting region 9 separately from the second wiring electrode35.

A film 10 is formed on the front face 103 side of the multilayerstructure LS2 so as to cover the photodetecting region 9 and contactelectrode 71. The glass substrate 1 is in contact with and attached tothe surface 10 a on the side opposite from the multilayer structure LS2in the film 10. The glass substrate 1 has a thickness of about 0.3 mm,and is optically transparent to incident light.

In the following, a method of manufacturing the semiconductorphotodetector device PD5 will be explained with reference to FIGS. 26 to32. FIGS. 26 to 32 are views for explaining the method of manufacturingthe semiconductor photodetector device PD5, and show a vertical sectionof the semiconductor photodetector device PD5.

This manufacturing method successively executes the following steps (1)to (10). Steps (1) and (2) are the same as steps (1) and (2) in thefirst embodiment, and thus will not be explained.

Step (3)

Next, a passivation film 19 made of SiN_(X) is formed on the front face103 of the cap layer 7 (multilayer structure LS2) by PCVD (see FIG. 26).

Step (4)

Next, a resist film (not depicted) having an opening at a positioncorresponding to the contact electrode 71 is formed, and the passivationfilm 19 is removed by buffered hydrofluoric acid (BHF) while using thisresist film as a mask, so as to form a contact hole 19 a in thepassivation film 19 (see FIG. 27). Subsequently, the resist film isremoved.

Next, a resist film (not depicted) having an opening at a positioncorresponding to the contact hole 19 a is formed again. Then, using thisresist film as a mask, a contact electrode 71 made of Ti/Pt/Au is formedby vapor deposition and liftoff on the part of photodetecting region 9exposed by the contact hole 19 a (see FIG. 27 as above). Subsequently,the resist film is removed.

Step (5)

Next, a film 10 is formed and flattened on the front face 103 side ofthe multilayer structure LS2 so as to cover the photodetecting region 9(passivation film 19) and contact electrode 71 (see FIG. 28). Here, thesurface 10 a positioned on the side opposite from the multilayerstructure LS2 in the film 10 is flattened as a front face of a structureincluding the multilayer structure LS2 and semiconductor substrate 51.The method of forming the film 10 is the same as the forming method instep (8) in the first embodiment.

Step (6)

Next, a glass substrate 1 is attached to the semiconductor substrate 51formed with the multilayer structure LS2, etching stop layer 2, and film10 (see FIG. 29). The method of attaching the glass substrate 1 is thesame as the attaching method in step (9) in the first embodiment.

Step (7)

Next, the semiconductor substrate 51 is removed. After the glasssubstrate 1 and semiconductor substrate 51 are attached to each other,the main face (rear face) 112 positioned on the side opposite from theglass substrate 1 in the semiconductor substrate 51 is exposed. Thisstep starts etching from the rear face 112 side of the semiconductorsubstrate 51, so as to remove the semiconductor substrate 51, bufferlayer 53, and etching stop layer 2 (see FIG. 30).

Specifically, an etchant exhibiting a lower etching rate to the etchingstop layer 2 is used at first, so as to remove the semiconductorsubstrate 51 and buffer layer 53. Subsequently, an etchant which canetch the etching stop layer 2 and exhibits a lower etching rate to theAlGaAs layer of the high-concentration carrier layer 3 is used, so as toremove the etching stop layer 2. This yields the glass substrate 1mounted with the multilayer structure LS2.

The method of etching the semiconductor substrate 51 and buffer layer 53is the same as the etching method in step (10) in the first embodiment.After etching the semiconductor substrate 51 and buffer layer 53, theglass substrate 1 with the remaining etching stop layer 2 and multilayerstructure LS2 is taken out of the mixed solution of NH₄OH and H₂O₂,washed with water, dried, and thereafter dipped in a mixed solution ofphosphoric acid (H₃PO₄), aqueous hydrogen peroxide, and water(H₃PO₄:H₂O:H₂O₂=4:90:1). Since AlGaAs is hardly etched by the mixedsolution of phosphoric acid, aqueous hydrogen peroxide, and water, onlythe etching stop layer 2 is etched, whereby the etching automaticallystops when the AlGaAs layer of the high-concentration carrier layer 3 isexposed. Thus, the etching stop layer 2 is removed. The semiconductorsubstrate 51, buffer layer 53, and etching stop layer 2 may be removedby chemical mechanical polishing (CMP) as well.

Step (8)

Next, a resist film (not depicted) having an opening at a position toform a through hole TH is formed on the high-concentration carrier layer3. Then, using this resist film as a mask, the multilayer structure LS2and passivation film 19 are etched (dry-etched) until the contactelectrode 71 is exposed. This forms the through hole TH (see FIG. 31).Subsequently, the resist film is removed. This dry etching is etching ofabout several micrometers and can be performed very easily.

Next, an electrically insulating film 20 made of SiN_(X) is formed onthe front face of the high-concentration carrier layer 3 by PCVD (seeFIG. 31). This forms the electrically insulating film 20 on the wallface of the multilayer structure LS2 defining the through hole TH.

Step (9)

Next, a resist film (not depicted) having an opening at a positioncorresponding to a contact electrode 83 is formed on the electricallyinsulating film 20. Then, using this resist film as a mask, theelectrically insulating film 20 is removed by BHF, so as to form acontact hole 20 b in the electrically insulating film 20 (see FIG. 31 asabove). Subsequently, the resist film is removed.

Next, a resist film (not depicted) having an opening at a positioncorresponding to the contact electrode 83 is formed. Then, using thisresist film as a mask, the contact electrode 83 made of Ti/Pt/Au isformed by liftoff (see FIG. 31 as above). Subsequently, the resist filmis removed.

Step (10)

Next, a resist film (not depicted) having openings at respectivepositions corresponding to a through lead 73 and a first pad electrode27 is formed on the electrically insulating film 20. Then, using thisresist film as a mask, the electrically insulating film 20 is removed byBHF, so as to form a contact film 20 a in the electrically insulatingfilm 20 (see FIG. 32). This exposes the contact electrode 71.Subsequently, the resist film is removed.

Next, a resist film (not depicted) having openings at respectivepositions corresponding to a first pad electrode 27 (through lead 73), asecond pad electrode 33, and a second wiring electrode 35 is formed.Then, using this resist film as a mask, the first pad electrode 27(through lead 73), second pad electrode 33, and second wiring electrode35 made of Ti/Pt/Au are formed by liftoff (see FIG. 32). The first padelectrode 27 and through lead 73 are formed integrally with each other.The second pad electrode 33 and second wiring electrode 35 are formedintegrally with each other. Subsequently, the resist film is removed.Thereafter, sintering is performed in an H₂ atmosphere. Though the firstpad electrode 27 and through lead 73 are formed integrally with eachother, they may be formed separately from each other. Similarly, thoughthe second pad electrode 33 and second wiring electrode 35 are formedintegrally with each other, they may be formed separately from eachother.

These steps (1) to (10) complete the semiconductor photodetector devicePD5 having the structure shown in FIGS. 24 and 25.

In this embodiment, as in the above-mentioned first embodiment, themechanical strength of the multilayer structure LS2 (laminatedhigh-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7) is held by the glass substrate 1 and film 10, while thesemiconductor photodetector device PD5 is easily made smaller. Also, thesemiconductor photodetector device PD5 can be mounted easily.

In this embodiment, the contact electrode 71 is electrically connectedto the first pad electrode 27 through the through lead 73 penetratingthrough the multilayer structure LS2. Using the through lead 73 canreliably conduct the contact layer 71 to the first pad electrode 27. Thesecond pad electrode 33 is electrically connected to thehigh-concentration carrier layer 3. Since an electrode is directly drawnfrom the high-concentration carrier layer 3, the series resistance cangreatly be reduced.

In the manufacturing method in accordance with this embodiment, theetching stop layer 2 is removed by wet etching after removing thesemiconductor substrate 51. The wet etching selectively removes theetching stop layer 2 alone by using an etchant which can etch theetching stop layer 2 but not the high-concentration carrier layer 3.Therefore, the etching stop layer 2 can be removed reliably and easilywhile leaving the multilayer structure LS2.

SIXTH EMBODIMENT

FIG. 33 is a schematic sectional view showing the structure of thesemiconductor photodetector device in accordance with a sixthembodiment. This semiconductor photodetector device PD6 differs from thesemiconductor photodetector device PD5 in accordance with the fifthembodiment in that the glass substrate 1 is formed with a lens part 121a.

The semiconductor photodetector device PD6 comprises a multilayerstructure LS2 and the glass substrate 1. This semiconductorphotodetector device PD6 is a photodetector device of front-illuminatedtype in which light is incident on the multilayer structure LS2 from theglass substrate 1 side. The semiconductor photodetector device PD6 is aphotodetector device for short-distance optical communications in thewavelength band of 0.85 μm, for example.

The lens part 121 a for converging incident light is formed on the frontface 121 of the glass substrate 1. The other part 121 b of the frontface 121 is thicker than the lens part 121 a. Namely, the lens part 121a is depressed from the thickest part 121 b of the front face 121.

Next, a method of manufacturing the semiconductor photodetector devicePD6 will be explained with reference to FIG. 34. FIG. 34 is a view forexplaining this manufacturing method, and shows a vertical section ofthe semiconductor photodetector device PD6.

This manufacturing method successively executes the following steps (1)to (10). Steps (1) to (5) are the same as steps (1) to (5) in the fifthembodiment, and thus will not be explained.

Step (6)

Next, the glass substrate 1 is attached to the semiconductor 51 formedwith the multilayer structure LS2, etching stop layer 2, and film 10(see FIG. 34). Specifically, the glass substrate 1 having the front face121 formed with the lens part 121 a is prepared, and the rear face 122of the glass substrate 1 is cleaned. Then, the glass substrate 1 and thesemiconductor substrate 51 are stacked such that the cleaned rear face122 of the glass substrate 1 and the surface 10 a remote from themultilayer structure LS2 in the film 10 are in contact with each other.Subsequently, the stacked glass substrate 1 and semiconductor substrate51 are pressed and heated, so as to attach the glass substrate 1 andfilm 10 to each other by fusion. Details of this attaching method arethe same as those in step (9) in the first embodiment.

Steps (7) to (10) are the same as steps (7) to (13) in the fifthembodiment, and thus will not be explained here. These steps (1) to (10)complete the semiconductor photodetector device PD6 having the structureshown in FIG. 33.

In this embodiment, as in the above-mentioned fifth embodiment, themechanical strength of the multilayer structure LS2 (laminatedhigh-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7) is held by the glass substrate 1 and film 10, while thesemiconductor photodetector device PD6 is easily made smaller. Also, thesemiconductor photodetector device PD6 can be mounted easily.

Since the glass substrate 1 is provided with the lens part 121 a, theincident light can be received efficiently even when the photodetectingregion 9 is smaller than the illuminating area of the incident light. Asa result, the semiconductor photodetector device PD6 with an excellentS/N ratio and high reliability can be obtained.

SEVENTH EMBODIMENT

FIG. 35 is a schematic sectional view showing the structure of thesemiconductor photodetector device in accordance with a seventhembodiment. This semiconductor photodetector device PD7 differs from thesemiconductor photodetector device PD5 in accordance with the fifthembodiment in that it has a film made of silicon oxide (SiO₂) or a resininstead of the glass substrate 1 and film 10.

The semiconductor photodetector device PD7 comprises the multilayerstructure LS2 and a film 60. The film 60 has two main faces opposingeach other, i.e., front face 131 and rear face 132. The multilayerstructure LS2 is provided on the rear face 132 of the film 60. Thissemiconductor photodetector device PD7 is a photodetector device offront-illuminated type in which light is incident on the multilayerstructure LS2 from the film 60 side. The semiconductor photodetectordevice PD7 is a photodetector device for short-distance opticalcommunications in the wavelength band of 0.85 μm, for example.

On the front face 103 of the multilayer structure LS2, the film 60 isformed such as to cover the photodetecting region 9 and the contactelectrode 71. The film 60 is made of silicon oxide or a resin (e.g.,polyimide resin, PMMA, or epoxy resin). The film 60 has a thickness ofabout 50 μm and is optically transparent to incident light.

A method of manufacturing the semiconductor photodetector device PD7will now be explained with reference to FIGS. 36 and 37. FIGS. 36 and 37are views for explaining this manufacturing method, and show a verticalsection of the semiconductor photodetector device PD7.

This manufacturing method successively executes the following steps (1)to (9). Steps (1) to (4) are the same as steps (1) to (4) in the fifthembodiment, and thus will not be explained.

Step (5)

Next, a film 60 is formed on the front face 103 side of the multilayerstructure LS2 so as to cover the photodetecting region 9 (passivationfilm 19) and contact electrode 71 (see FIG. 36). The method of formingthe film 60 is the same as the forming method in step (8) in the thirdembodiment.

Step (6)

Next, the semiconductor substrate 51 is removed. The main facepositioned on the side opposite from the film 60 in the semiconductorsubstrate 51, i.e., the rear face 112, is exposed after forming the film60. This step removes the semiconductor substrate 51 and etching stoplayer 2 by etching from the rear face 112 side of the semiconductorsubstrate 51 (see FIG. 37). The method of etching the semiconductorsubstrate 51 and etching stop layer 2 is the same as the etching methodin step (7) in the above-mentioned fifth embodiment.

Steps (7) to (9) are the same as steps (8) to (10) in the fifthembodiment, and thus will not be explained here. These steps (1) to (9)complete the semiconductor photodetector device PD7 having the structureshown in FIG. 35.

In this embodiment, as in the above-mentioned fifth embodiment, themechanical strength of the multilayer structure LS2 (laminatedhigh-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7) is held by the film 60, while the semiconductor photodetectordevice PD7 is easily made smaller. Also, the semiconductor photodetectordevice PD7 can be mounted easily.

EIGHTH EMBODIMENT

FIG. 38 is a schematic sectional view showing the structure of thesemiconductor photodetector device in accordance with an eighthembodiment. This semiconductor photodetector device PD8 differs from thesemiconductor photodetector device PD7 in accordance with the seventhembodiment in that the film 60 is formed with a lens part 131 a.

The semiconductor photodetector device PD8 comprises the multilayerstructure LS2 and the film 60. This semiconductor photodetector devicePD8 is a photodetector device of front-illuminated type in which lightis incident on the multilayer structure LS2 from the film 60 side. Thesemiconductor photodetector device PD8 is a photodetector device forshort-distance optical communications in the wavelength band of 0.85 μm,for example.

The front face 131 of the film 60 is formed with the lens part 131 a forconverging incident light. The lens part 131 a can be formed by wetetching. The wet etching for forming the lens part 131 a is the same asthe wet etching method explained in the above-mentioned fourthembodiment.

In this embodiment, as in the above-mentioned fifth embodiment, themechanical strength of the multilayer structure LS2 (laminatedhigh-concentration carrier layer 3, light-absorbing layer 5, and caplayer 7) is held by the film 60, while the semiconductor photodetectordevice PD8 is easily made smaller. Also, the semiconductor photodetectordevice PD8 can be mounted easily.

Since the film 60 is provided with the lens part 131 a, the incidentlight can be received efficiently even when the photodetecting region 9is smaller than the illuminating area of the incident light. As aresult, the semiconductor photodetector device PD8 with an excellent S/Nratio and high reliability can be obtained.

Modified examples of these embodiments will now be explained withreference to FIGS. 39 and 40. These modified examples are semiconductorphotodetector device arrays PDA1 and PDA2 in which a plurality ofphotodetecting regions 9 are provided in a row. These photodetectordevice arrays PDA1 and PDA2 are of so-called front-illuminated type.

In the photodetector array PDA1, a plurality of photodetecting parts 11and photodetecting regions 9 are arranged one- or two-dimensionally asshown in FIG. 39. In the photodetector array PDA2, a plurality ofphotodetecting regions 9 are arranged one- or two-dimensionally as shownin FIG. 40.

In the photodetector array PDA1, the mechanical strength of themultilayer structure LS1 (laminated high-concentration carrier layer 3,light-absorbing layer 5, and cap layer 7) is held by the glass substrate1 as in the above-mentioned first embodiment. Also, the pitch betweenthe photodetecting parts 11 and the pitch between the photodetectingregions 9 can be narrowed, whereby the photodetector array PDA1 iseasily made smaller.

In the photodetector array PDA2, the mechanical strength of themultilayer structure LS2 (laminated high-concentration carrier layer 3,light-absorbing layer 5, and cap layer 7) is held by the glass substrate1 as in the above-mentioned fifth embodiment. Also, the pitch betweenthe photodetecting regions 9 can be narrowed, whereby the photodetectorarray PDA2 is easily made smaller.

In the photodetector arrays PDA1 and PDA2, the above-mentioned film 60may be provided instead of the glass substrate 1 and film 10. Lens parts(e.g., the above-mentioned lens parts 121 a and 131 a) may be formed soas to correspond to the respective photodetecting regions 9.

An optical interconnection system using the above-mentionedsemiconductor photodetector device (or photodetector array) will now beexplained with reference to FIG. 41. FIG. 41 is a schematic view showingthe structure of the optical interconnection system.

The optical interconnection system 151 is a system for transmittingoptical signals between a plurality of modules (e.g., CPUs, IC chips,and memories) M1 and M2, and includes a semiconductor light-emittingdevice 153, a driving circuit 155, an optical waveguide substrate 157, asemiconductor photodetector device PD1, an amplifying circuit 159, andthe like. A vertical cavity surface emitting laser (VCSEL) ofback-illuminated type can be used as the semiconductor light-emittingdevice 153. The module M1 is electrically connected to the semiconductorlight-emitting device 103 through bump electrodes. The driving circuit155 is electrically connected to the semiconductor light-emitting device103 through bump electrodes. The semiconductor photodetector device PD1is electrically connected to the amplifying circuit 159 through bumpelectrodes 41. The amplifying circuit 159 is electrically connected tothe module M2 through bump electrodes.

An electric signal outputted from the module M1 is sent to the drivingcircuit 155, and is converted into an optical signal by thesemiconductor light-emitting device 153. The optical signal from thesemiconductor light-emitting device 153 passes through an opticalwaveguide 157 a on the optical waveguide substrate 157, so as to be madeincident on the semiconductor photodetector device PD1. The opticalsignal is converted by the semiconductor photodetector device PD1 intoan electric signal, which is then sent to the amplifying circuit 109 andamplified therein. The amplified electric signal is sent to the moduleM2. Thus, the electric signal outputted from the module M1 istransmitted to the module M2.

Any of the semiconductor photodetector devices PD2 to PD8 orsemiconductor photodetector device arrays PDA1 and PDA2 may be used inplace of the semiconductor photodetector device PD1. When thesemiconductor photodetector device array PDA1, PDA2 is used, thesemiconductor light-emitting device 153, driving circuit 155, opticalwaveguide substrate 157, and amplifying circuit 159 are also arranged soas to form an array.

The present invention is explained in detail with reference to itsembodiments in the foregoing. However, the present invention is notlimited to the above-mentioned embodiments. The present invention can bemodified in various ways within a scope not deviating from its gist. Forexample, thicknesses, materials, and the like of the semiconductorsubstrate 51, high-concentration carrier layer 3 (3 a, 3 b),light-absorbing layer 5 (5 a, 5 b), cap layer (7 a, 7 b), and the likeare not limited to those mentioned above. Specifically, Si, InP, InGaAs,InSb, or InAsSb may be used as a material of the semiconductor substrate51 instead of GaAs mentioned above.

From the invention thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the scope of the invention, and all such modifications aswould be obvious to one skilled in the art are intended to be includedwithin the following claims.

INDUSTRIAL APPLICABILITY

The present invention can provide a semiconductor photodetector devicewhich can be made smaller while having a sufficient mechanical strength,and a method of manufacturing the same. Also, the present inventionallows the semiconductor photodetector device to be mounted easily.

1. A photodetector device comprising: a multilayer structure including aplurality of compound semiconductor layers laminated and having firstand second main faces opposing each other; a photodetecting regionformed near the first main face within the multilayer structure; a firstelectrode arranged on the first main face of the multilayer structureand electrically connected to the photodetecting region; a secondelectrode arranged on the second main face of the multilayer structureand electrically connected to the first electrode; a third electrodearranged on the second main face of the multilayer structure andelectrically connected to a part near the second main face in themultilayer structure; and a light-transmitting layer, opticallytransparent to incident light and arranged on the first main face of themultilayer structure, covering the photodetecting region and firstelectrode.
 2. A photodetector device according to claim 1, wherein thelight-transmitting layer includes a film made of silicon oxide and aglass substrate; and wherein the glass substrate is secured to themultilayer structure through the film made of silicon oxide.
 3. Aphotodetector device according to claim 1, wherein thelight-transmitting layer includes a film made of silicon oxide or aresin.
 4. A photodetector device according to claim 1, wherein theplurality of compound semiconductor layers include a high-concentrationcarrier layer of a first conductive type, a light-absorbing layer of thefirst conductive type, and a cap layer of the first conductive type; andwherein the photodetecting region is a region of a second conductivetype including at least a part of the cap layer.
 5. A photodetectordevice according to claim 4, wherein the multilayer structure furthercomprises a depression formed about the photodetecting region, and awiring electrode arranged within the depression; wherein the firstelectrode is electrically connected to the second electrode through thewiring electrode; and wherein the third electrode is electricallyconnected to a part positioned near the photodetecting region in thehigh-concentration carrier layer.
 6. A photodetector device according toclaim 4, further comprising a through lead penetrating through themultilayer structure; wherein the first electrode is electricallyconnected to the second electrode through the wiring electrode; andwherein the third electrode is electrically connected to thehigh-concentration carrier layer.
 7. A photodetector device according toclaim 1, wherein the second and third electrodes include respective padelectrodes, while respective bump electrodes are arranged on the padelectrodes.
 8. A photodetector device according to claim 1, furthercomprising a light-reflecting film, provided on the second main face,covering the photodetecting region.
 9. A photodetector device accordingto claim 1, comprising a plurality of photodetecting regions arranged ina row.
 10. A photodetector device according to claim 1, wherein thelight-transmitting layer includes a lens part converging the incidentlight.
 11. A method of manufacturing a semiconductor photodetectordevice, the method comprising the steps of: preparing a semiconductorsubstrate; providing a multilayer structure on the semiconductorsubstrate, the multilayer structure including a plurality of compoundsemiconductor layers laminated and having first and second main facesopposing each other, the second main face facing the semiconductorsubstrate; forming a photodetecting region near the first main facewithin the multilayer structure; providing a first electrodeelectrically connected to the photodetecting region onto the first mainface of the multilayer structure; forming a light-transmitting layeroptically transparent to incident light onto the first main face of themultilayer structure so as to cover the photodetecting region and firstelectrode; removing the semiconductor substrate after forming thelight-transmitting layer; and forming a second electrode electricallyconnected to the first electrode onto the second main face of themultilayer structure while forming a third electrode electricallyconnected to a part near the second main face in the multilayerstructure onto the second main face after removing the semiconductorsubstrate.
 12. A method of manufacturing a semiconductor photodetectordevice according to claim 11, wherein the step of forming thelight-transmitting layer includes the steps of: forming a film made ofsilicon oxide so as to cover the photodetecting region and firstelectrode; and securing a glass substrate optically transparent to theincident light onto the film made of silicon oxide.
 13. A method ofmanufacturing a semiconductor photodetector device according to claim11, wherein the step of forming the light-transmitting layer includesthe step of forming a film made of silicon oxide or a resin so as tocover the photodetecting region and first electrode.
 14. A method ofmanufacturing a semiconductor photodetector device according to claim11, wherein the step of removing the semiconductor substrate includesthe step of removing the semiconductor substrate by wet etching; andwherein the step of forming the multilayer structure includes the stepof forming an etching stop layer for stopping wet etching between thesemiconductor substrate and the plurality of compound semiconductorlayers.
 15. A method of manufacturing a semiconductor photodetectordevice according to claim 14, further comprising the step of removingthe etching stop layer by wet etching after removing the semiconductorsubstrate.
 16. A method of manufacturing a semiconductor photodetectordevice according to claim 11, wherein the plurality of compoundsemiconductor layers include a high-concentration carrier layer of afirst conductive type, a light-absorbing layer of the first conductivetype, and a cap layer of the first conductive type; wherein the step offorming the multilayer structure includes the step of successivelylaminating the high-concentration carrier layer, light-absorbing layer,and cap layer on the semiconductor substrate; and wherein the step offorming the photodetecting region includes the step of forming a regionof a second conductive type including at least a part of the cap layeras the photodetecting region.
 17. A method of manufacturing asemiconductor photodetector device according to claim 16, furthercomprising the steps of forming a depression about the photodetectingregion; and providing a wiring electrode for electrically connecting thefirst electrode to the second electrode in the depression; wherein thestep of forming the third electrode includes the step of forming thethird electrode such that the third electrode is electrically connectedto a part positioned near the photodetecting region in thehigh-concentration carrier layer.
 18. A method of manufacturing asemiconductor photodetector device according to claim 16, wherein thestep of forming the second electrode includes the step of forming athrough lead penetrating through the multilayer structure, andelectrically connecting the first electrode to the second electrodethrough the through lead; and wherein the step of forming the thirdelectrode includes the step of forming the third electrode such that thethird electrode is electrically connected to the high-concentrationcarrier layer.
 19. A method of manufacturing a semiconductorphotodetector device according to claim 11, further comprising the stepof forming a light-reflecting film covering the photodetecting regiononto the second main face of the multilayer structure.
 20. A method ofmanufacturing a semiconductor photodetector device according to claim11, wherein the light-transmitting layer includes a lens part convergingthe incident light.